Railroad freight cars in the United States have almost exclusively employed double axle four wheel trucks. In recent years, however, freight cars for relatively light loads, such as piggy back trailers and containers, have employed single axle two wheel trucks at each end. The U.S. patents of Brodeur et al U.S. Pat. No. 4,596,311 and Terlecky U.S. Pat. No. 4,636,119 disclose such railroad cars.
The Brodeur et al U.S. Pat. No. 4,596,311 discloses a particular type of single axle two wheel truck having a truck frame fabricated with two transverse beams and two side tubes. The railroad car center sill is supported at each end by the frames of such trucks. The springs and wheel assembly of each truck are operatively connected to the frame. One such truck in commercial use is conventionally referred to as a U.I.C. or International Union of Railways truck.
Conventional construction of a railroad car with such a truck is to apply the axle guard, which limits horizontal, vertical and lateral movement of the truck axle, as a subassembly to each of the longitudinal spaced apart side tubes. This is not readily accomplished, however, because of tight tolerances between centers of the two transverse beams, axle guard and the side tubes. Also, the ends of the tubes required beveling for welding and sometimes the tube ends had to be cut to an intricate contour when the beam did not provide an abutting planar or flat surface.
In addition, it is not unusual for the frames of such single axle trucks to be damaged in use and to require replacement of one or more transverse beams and side tubes. This is not readily done with frames having the present construction.
From the above it is clear that a new frame construction is needed for single axle two wheel trucks which are readily fabricated initially and easily repaired later if damaged.